<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <input type="button" value="点击显示图片" id="bn">
    <img src="" alt="" id="im" />
    <script>
    
    document.getElementById("bn").onclick = function (){
        var imObj =  document.getElementById("im");
        imObj.src = "img/liuyan.jpg";
        imObj.width = 500;
        imObj.height = 400;
    }

    </script>
</body>
</html>